Patent GB-191500939-A (GB)
Title: Improvements Circuit Arrangements for Telephone Systems.
Inventor: IMRAY OLIVER
Filed: 1915-01-20
Granted: 1915-12-02
Abstract: 939. Imray, O., [Siemens & Halske Akt.-Ges.]. Jan. 20. Semi-automatic exchange systems.-The same switches VW and junction lines a, b serve for both the incoming and outgoing calls of a group of subscribers. In the case of outgoing calls, the switches VW act in the ordinary way as preliminary selectors to connect the calling line to an idle junction line. In the case of incoming calls, an operator presses keys SP, NT individual to the calling junction line and to the wanted subscriber's line, thereby setting in action the switch VW of the wanted line and marking all except the calling junction line non-selectable to it. In the arrangement shown in Fig. 1, the operation of the switch VW for outgoing and incoming calls is controlled over separate test circuits c, d; but a modification is described in which both operations are controlled over the same test wiper. The invention is specially applicable for dealing with calls between a private hranch exchange and a main exchange. Local interconnexions. When a private branch exchange subscriber N lifts down his receiver, the line relay R closes the circuit of the stepping-magnet D, which rotates the switch VW until an idle junction line is fonnd, the cut-off relay T being then energized in series with a relay C over the circuit c. The relay T stops the switch and locks itself over its second winding, and the relay C locks itself under control of a relay S, which is energized over the calling line and closes the circuit of the call lamps AN. The branch operator depresses her speaking-key SC to learn the connexion desired ; if this is a local one, she sets it up over jack K by means of a cord circuit the usual way. Outgoing calls to main exchange. If a mainexchange connexion is required. The operator momentarily presses the key SP, thus energizing a relay F. which locks up under the control of the relay S and completes at contact 39 the outgoing circuit 71, 72 so as to signal the operator at the main exchange. Incoming calls from main exchange. The application of ringing-current to the line l1, l2 energizes a relay A, which controls a relay H, which locks itself up and Jights a call lamp AL. The local operntor answors the call by pressing the speaking-key SP, which energizes the relay F so as to complete the circuit l1, l2 at the contact 39, at the same time unlocking the relay H so as to extinguish the lamp AL. Having ascertained which subscriber is wanted, she presses a key NT individual to his line, and under the joint control of the keys NT, SP, the desired connexion is completed by the wanted - subscriber's selector VW, as follows. The relay F, energized by the key SP, transfers the relay C from the circuit c to the circuit d, so that the junction line l1, 12 is rendered selectable only to a switch VW testing over its fourth wiper, while the key NT starts the switch VW of the wanted line and transfers its test circuit to the fourth wiper, so that it is forced to select the line l1, 12. While the switch VW is in motion, a common relay G is energized and opens the normal test circuits of all the junction lines at the contact 28, so that they all test busy to any switch VW which may be set in action to extend an outgoing call. The relay G also energizes a relay E, which energizes a relay Z and prepares the circuit of the ringing-relay L. When the switch VW reaches the line l1, l2, the relays T, C are energized in series over the fourth wiper. The relay T stops the switch, de-energizes the relay G, and locks itself over its second winding. The relay C completes the periodic circuit of the ringing-relay L and locks the relay E independently of the relay G. At cach de-energization of the ringing-relay L, a tell-tale lamp BL is flashed. When the subscriber N replies to the call, the relay S is energized and open-circuits the relay E, which stops the ringing. The relay C, which has thus far been energized over the contact 19 of the relay E. is now maintained by the contact 36 of the relay S. The relay S also locks the relay F independently of the key SP and maintains the energization of the relay Z. Release. Disconnexion is effected by the relay S unlocking the relays T, C when the subscriber N hangs up his instrument. To prevent the confusion which might arise from a calling branch exchange subscriber becoming connected to a junction line at the moment of its release from a previous connexion, the following means are provided for marking a junction line busy for a certain interval after its release, the interval being sufficient to ensure that the main-exchange operator will have disconnected the junction line at its far end. The relay F, when it is energized by the operator answering a call, energizes a relay B, which controls the stepping-magnet D1 of a timeswitch VS. The switch is thus moved a step from normal and de-energizes the relay T3. which stops it again. When the relay F is de-energized by the release of the connexion, it again energizes the relay B and sets the switch VS in action. The relay B remains energized until the switch VS regains its normal position, and during this interval, it marks the line l1, 72 non-selectable by opening its test circuit at the contact 41. Interrupting connexions in favour of preferred calls. For this purpose, each junction line is provided with a key TR by which the local operator can sever a connexion. Signalling to operator. The subscriber N has a signalling-key Ts, which operates a differential relay M by upsetting the balance of current in the line a, b. The relay M either operates a local signal lamp ML or signats the main exchange by opening the line l1, l2, according as the relay Z is energized or not, which depends on whether the call is from or to the main exchange. Controlling the switch VW over the same test wiper for both incoming and outgoing calls. This may be effected by arranging the common relay G to open the normal drive and test circuits of all the switches VW, so that while one of these switches is completing an incoming call, none of them can be set in action to extend an outgoing call.